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P.A. PSARAS** AND H.T.G. HENTZELL* Dept. of Physics and Measurement Technology,

Link6ping, Sweden **IBM, Thomas J. Watson Research Center,

Yorktown Heights,

S-58183

New York,

10598

USA

ABSTRACT The crystallization of s-Si in a-Si(50nm) and Au(5nm) thin film bilayers has been investigated during heat treatment in a transmission elect0 ron microscope (TEM). When crystallization of c-Si first begins at 130 C the Au-Si alloy reflections observed at lower temperatures vanish and several new reflections from metastable Au-Si compounds occur. Dendritically 0 growing islands of poly-Si are observed after heating at 175 C. If the 0 samples are held constant at 175 C for ten minutes, the poly-Si islands grow together. The formation of poly-Si depends on the diffusion of Au into c-Si and the formation of metastable Si-Au compounds. After crystallization Au segregates to the front and back surface of the poly-Si film.

INTRODUCTION Metal-semiconductor interaction is a subject of considerable interest from fundamental physics and technological view-points. In the past, the focus of most research has been metal-single crystal semiconductor reactions [1-5). Recently interest has turned to metal-amorphous semiconductor interfaces [6), for the purpose of studying any differences in the interaction at the interface that might depend on the order of the atoms of the semiconductor. With regard to metal-single crystal semiconductor bilayers of Si/Au, electron spectroscopy studies show that although no definite compounds are formed, some intermixing takes place, giving Si a metallic nature [1-5). Green and Bauer [7] confirmed the existence of gold silicides at the interface at elevated temperatures. Several types of metastable gold silicides have also been observed in gold-silicon alloys [8-14]. For metal-amorphous silicon, very few studies of the interaction at the interface have been performed. Thompson et al. [6] studied the reaction between Au, Al, Pd, Pt and c-Si:H and found that Au and Al in particular 0 cause crystallization of the c-Si:H at temperatures less than 250 C (for 0 Si Tc : 630 C). In the present work, we have studied the interaction between Au and evaporated s-Si at temperatures between Room Temperature (RT) 0 and the Au-Si eutectic temperature (363 C) in order to observe the initial reaction between Au and c-Si and the catalyzing effect of Au on the crystallization of s-Si.

EXPERIMENTAL DETAILS The thin film bilayers of 50 nm c-Si and 5 nm Au were evaporated with the use of an'electron beam on Si 34N -windows at a base pressure of 5x10-7 torr. The films were deposited consecutively without breaking the vacuum. The microstructure and phase formation in the c-Si/Au thin film couples were studied in a transmission electron microscope. These samples were 0 annealed at temperatures between RT and 658 C in the TEM. A resistively heated sample holder was used where the temperature readings were adjusted against a temperature calibration curve derived from three references; RT, 0 the eutectic temperature of Au-Si (36